Complete Genome Sequence of Citrobacter freundii Myophage Michonne

Isolation and characterization of the new isolated bacteriophage YZU-L1 against Citrobacter freundii from a package-swelling of meat product

Citrobacter freundii is an important foodborne pathogen that can cause urethritis, bacteremia, necrotizing abscess, and meningitis in infants. In this study, a gas-producing isolate from vacuum-packed meat products was identified as C. freundii by 16S rDNA. In addition, a new virulent phage YZU-L1, which could specifically lyse C. freundii, was isolated from sewage samples in Yangzhou. Transmission electron microscopy showed that phage YZU-L1 had a polyhedral head of 73.51 nm in diameter and a long tail of 161.15 nm in length. According to phylogenetic analysis employing the terminase large subunit, phage YZU-L1 belonged to the Demerecviridae family and the Markadamsvirinae subfamily. The burst size was 96 PFU/cell after 30 min of latent period and 90 min of rising period. Phage YZU-L1 could maintain high activity at pH of 4-13, and resist 50 °C for up to 60 min. The complete genome of YZU-L1 was 115,014 bp double-stranded DNA with 39.94% G + C content, encoding 164 open reading frames (ORFs), without genes encoding for virulence, antibiotic resistance, or lysogenicity. Phage YZU-L1 treatment significantly reduced the viable bacterial count of C. freundii in a sterile fish juice model, which is expected to be a natural agent for the biocontrol of C. freundii in foods.

The Bacteriophage vB_CbrM_HP1 Protects Crucian Carp Against Citrobacter braakii Infection

Citrobacter braakii is an opportunistic pathogen that induces aquatic infections in fish and turtles. In this study, a bacteriophage that infects C. braakii, named vB_CbrM_HP1, was isolated from sewage. This phage belongs to Myoviridae family, Ounavirinae subfamily, Mooglevirus genus. We also used the phage to treat crucian carp infection caused by C. braakii for the first time. vB_CbrM_HP1 was relatively stable at temperatures ranging from 4 to 60°C and pH values ranging from 3 to 11 but float slightly. When the multiplicities of infection (MOI) was 0.0001, the titer reached a maximum of 4.20 × 1010 PFU/ml. As revealed from the results of whole genomic sequence analysis, the total length of vB_CbrM_HP1 was 89335 bp, encoding 135 ORFs, 9 of which were <75% similar to the known sequences in NCBI. The phage vB_CbrM_HP1 showed a highly efficient bactericidal effect against C. braakii both in vitro and in vivo. In vitro, vB_CbrM_HP1 was capable of effectively killing bacteria (the colony count decreased by 4.7 log units at 5 h). In vivo, administration of vB_CbrM_HP1 (1 × 109 PFU) effectively protected crucian carp against fatal infection caused by C. braakii. Phage treatment reduced the levels of inflammatory factors. All these results demonstrated the potential of vB_CbrM_HP1 as an alternative treatment strategy for infections caused by C. braakii.

Isolation and Characterization of Bacteriophages That Infect Citrobacter rodentium, a Model Pathogen for Intestinal Diseases

Enteropathogenic Escherichia coli (EPEC) is a major pathogen for diarrheal diseases among children. Antibiotics, when used appropriately, are effective; however, their overuse and misuse have led to the rise of antibiotic resistance worldwide. Thus, there are renewed efforts into the development of phage therapy as an alternative antibacterial therapy. Because EPEC in vivo models have shortcomings, a surrogate is used to study the mouse pathogen Citrobacter rodentium in animal models. In this study, two new phages CrRp3 and CrRp10, which infect C. rodentium, were isolated and characterized. CrRp3 was found to be a new species within the genus Vectrevirus, and CrRp10 is a new strain within the species Escherichia virus Ime09, in the genus Tequatrovirus. Both phages appear to have independently evolved from E. coli phages, rather than other Citrobacter spp. phages. Neither phage strain carries known genes associated with bacterial virulence, antibiotic resistance, or lysogeny. CrRp3 is more potent, having a 24-fold faster adsorption rate and shorter lytic cycle when compared to the same properties of CrRp10. However, a lysis curve analysis revealed that CrRp10 prevented growth of C. rodentium for 18 h, whereas resistance developed against CrRp3 within 9 h. We also show that hypoxic (5% oxygen) conditions decreased CrRp3 ability to control bacterial densities in culture. In contrast, low oxygen conditions did not affect CrRp10 ability to replicate on C. rodentium. Together, CrRp10 is likely to be the better candidate for future phage therapy investigations.

Complete Genome Sequence of Citrobacter freundii Myophage Mijalis

Citrobacter freundii is responsible for various opportunistic nosocomial infections. Phage therapies against C. freundii may prove useful in human medicine for treatment of infections caused by the ubiquitous bacteria. Here, we announce the complete genome sequence of the C. freundii Felix O1-like myophage Mijalis and present its features.

Characterization of Five Podoviridae Phages Infecting Citrobacter freundii

Citrobacter freundii causes opportunistic infections in humans and animals, which are becoming difficult to treat due to increased antibiotic resistance. The aim of this study was to explore phages as potential antimicrobial agents against this opportunistic pathogen. We isolated and characterized five new virulent phages, SH1, SH2, SH3, SH4, and SH5 from sewage samples in Tunisia. Morphological and genomic analyses revealed that the five C. freundii phages belong to the Caudovirales order, Podoviridae family, and Autographivirinae subfamily. Their linear double-stranded DNA genomes range from 39,158 to 39,832 bp and are terminally redundant with direct repeats between 183 and 242 bp. The five genomes share the same organization as coliphage T7. Based on genomic comparisons and on the phylogeny of the DNA polymerases, we assigned the five phages to the T7virus genus but separated them into two different groups. Phages SH1 and SH2 are very similar to previously characterized phages phiYeO3-12 and phiSG-JL2, infecting, respectively, Yersinia enterocolitica and Salmonella enterica, as well as sharing more than 80% identity with most genes of coliphage T7. Phages SH3, SH4, and SH5 are very similar to phages K1F and Dev2, infecting, respectively, Escherichia coli and Cronobacter turicensis. Several structural proteins of phages SH1, SH3, and SH4 were detected by mass spectrometry. The five phages were also stable from pH 5 to 10. No genes coding for known virulence factors or integrases were found, suggesting that the five isolated phages could be good candidates for therapeutic applications to prevent or treat C. freundii infections. In addition, this study increases our knowledge about the evolutionary relationships within the T7virus genus.